I used RO/DI water in my 100g frag tank system and put live rock in it from my main tank (which holds the bacteria you want). 7 Days later I had sps frags in there and 10 days from initial set up had a sailfin tang in there. Everything has done great. THe big key is using live rock from your DT which has the bacteria needed to do the break down of ammonia and nitrites. The water doesn't make a difference as the bacteria aren't grouped up in the water column like they hold to live rock.